Recently, a small-hole electrical discharge machining device is widely used for machining such a hole or holes as an initial hole for processing to thread a wire electrode of wire-cut electrical discharge machining, a hole of a component for an aircraft or an automobile and the like, because the small-hole electrical discharge machining device achieves the faster machining speed compared to a die sinking electric discharge machining device.
The small-hole electrical discharge machining device in such a manner as flushing the working fluid, is able to produce a small hole or holes some ten times as deep as the electrode diameter(s) at a high speed by electrical discharge machining in which an stick-shaped or pipe-shaped electrode(s) are applied and pulse voltage is applied to the portion between a tip surface of the electrode-for-machining and a segment of the workpiece opposite to the electrode to repeat pulse discharge with a electrode-for-machining cooled by supplying working fluid to a machining area of a workpiece.
Pressurized working fluid applied to the machining area (the machined hole) discharges machining debris generated by the electrical discharge machining, gas and the like from the entrance of the electrical discharge machined hole through an electrical discharge machining gap (the gap between a diameter of the electrode and a diameter of the hole of the workpiece).
Though the supply of the working fluid is needed for cooling the electrical discharge machining gap between the electrode and the workpiece and for promotion of discharge of the machining debris and gas and for the like, the supply of a great deal of the fluid to the electrical discharge gap is very difficult when machining a narrow and deep hole. Therefore, conventionally, supply pump pressure of the working fluid was increased and the pressurized fluid was attempted to supply, but it was difficult to supply and circulate the sufficient working fluid because the hole was narrow and deep. Furthermore, the machining debris has a tendency to be fused and accumulate as fused adhesive deposits at the corner portion of the opening in an entrance side of the machined hole
As shown in FIG. 5, in the prior art, the working fluid was jetted through the pipe electrode and toward the obliquely downward electrical discharge machining area by a jet nozzle of the working fluid disposed apart from the electrode. Specifically, also in the drilling electrical discharge machining, the jet from the side by employing the jet nozzle is adopted for discharge and removal of the machining debris in a periphery of the machining area. When applying the stick-shaped electrode, the working fluid is jetted with the jet nozzle disposed obliquely upward of the electrode, but at least a half of the opening in an entrance side of the machining area of the workpiece is submerged in the jetted working fluid, discharge openings of the machined chips are normally concentrated at a part in the opposite side of the jetting direction, and secondary discharge are generated frequently with such a low machining efficiency, such a machining system has a problem that the machined hole becomes ellipsoidal shape which have a long axis along with the jetting direction of the working fluid.
Furthermore, when the jet pressure of the working fluid is increased for the purpose of improvement of the discharge performance of the machining debris, the force vector which pushes the side of the electrode increases, the electrical discharge machining becomes unstable because the electrode is moved to the jet direction of the opening and is vibrated, and the overlap of the mechanical factor and the secondary discharge phenomenon for lack of the quantity of the working fluid causes the formation of the ellipsoidal hole.
In the Patent Literature 1, the small-hole electrical discharge machining device holding an upper edge portion of a thin pipe electrode with a electrode holder which can feed to a direction of Z axis and be driven rotatively, guiding a bottom portion of the pipe electrode, performing the electrical discharge machining by rotating the pipe electrode and feeding it to the direction to Z axis while jetting the working fluid into the electrical discharge machined hole from an upper edge of the pipe electrode through the inside of the pipe electrode, and separately from the above mentioned supply of the working fluid, flushing away chips adhered on a corner portion of the opening in the entrance side of the machined hole by jetting the working fluid from the jet nozzle provided at a plurality of parts obliquely upward of the electrical discharge machined hole at a pressure of at least 2 MPa or more, and preventing the generation of the fused adhesive deposits, is proposed.
In the Patent Literature 2, the small-hole electrical discharge machining device holding the thin pipe electrode by a hollow spindle which can feed in a direction of Z axis and be driven rotatively is proposed. In the Patent Literature 2, the electrode guide guiding the bottom portion of the pipe electrode shown in Patent Literature 1 isn't disclosed. The electrical discharge machining is performed by rotating the pipe electrode and feeding it in a direction of Z axis while supplying the working fluid into the electrical discharge machined hole in a jet flow condition from the upper edge of the pipe electrode through the inside of the pipe electrode. The machining debris are discharged from the electrical discharge machining gap between the electrode and the workpiece by applying the working fluid through the inside of the pipe electrode in a jet condition into the electrical discharge machined hole so that the working fluid passed in the pipe electrode is pulsated at a frequency of 1.5 Hz or more.
In Patent Literature 3 and 4, the supply system of the pressurized working fluid in which the pressurized working fluid is supplied so as to surround the stick-shaped electrode or the pipe-shaped electrode, and in case of the pipe electrode, supplying the working fluid by way of its tubular space is also applied jointly, is adopted.
In the Patent Literature 3, the small-hole electrical discharge machining device which performs the small-hole electrical discharge machining by holding the upper edge of the stick-shaped or the pipe-shaped electrode with the electrode holder which can feed in a Z axis direction and be driven rotatively, and guiding the bottom portion of the pipe electrode with the electrode guide, supplying the pressurized working fluid from the upper edge of the electrode to the electrode holder with the circumference of the electrode surrounded, and supplying it in a jet condition from the electrode holder to the bottom edge of the electrode holder through a guide opening trough which the electrode passes arranged on the electrode holder with the circumference of the electrode surrounded, is proposed.
In the Patent Literature 4, the small-hole electrical discharge machining device which performs the small-hole electrical discharge machining by holding the upper edge of the stick-shaped or the pipe electrode with the electrode holder which can feeds in a Z axis direction and be driven rotatively, and guiding the bottom portion of the pipe electrode with the electrode guide, supplying the pressurized working fluid from the upper edge of the electrode to the electrode holder with the circumference of the electrode surrounded, getting mixed high pressure gas in the pressurized working fluid which is supplied to the electrode holder with the ejector mechanism arranged in the electrode holder, supplying the pressurized working fluid including the gas to the bottom edge of the electrode through the guide opening of the electrode guide with the circumference of the electrode surrounded, securing the workpiece in the vacuum suction box, performing the electrical discharge machining with the inside of the box vacuuming by suctioning from the bottom portion of the box with a vacuum suction apparatus, is proposed.